Devices of the type described above are used in a variety of applications. One example is the provision of haptic feedback in touch sensitive devices. Here, the transducers are controlled to cause the panel to vibrate in order to provide haptic feedback to a user in response to the device being touched. The same panel may be used in the detection of touch. The same transducers may be used for sensing touch as the transducers used for generating the haptic feedback. Alternatively separate transducers may be provided for touch sensing and haptic feedback generation respectively.
Vibratory panels, i.e. panels capable of producing or detecting vibrations, are also used in the generation and/or sensing of audio signals. Thus devices comprising such panels may be used as, or form part of, speakers and/or microphones.
A common use of haptic feedback is in hand held electronic devices such as phones and other communications devices having touch sensitive screens. The haptic feedback is provided to the user to confirm that a touch has been detected. A typical device capable of providing haptic feedback comprises a vibratory panel and two transducers mounted with respect to the panel so as to cause the panel to vibrate when energised. Electrical signals to be applied to the transducers are typically generated by a control chip providing signals on respective channels. The use of two transducers allows the possibility of “steering” the feedback in one dimension, i.e. to control to some degree the point on the screen where the haptic feedback vibration peaks. This can be done by using the relative strengths of signals applied to the two transducers to control the point on the screen at which the peak of the vibration occurs.
In some situations it is desired for haptic feedback to be silent. In principle, with a two channel system, this could be achieved by ensuring that the signals on the two channels are out of phase. However, no steering would then be possible. It would therefore be advantageous to be able to reduce acoustic output in a haptic feedback system whilst still being able to steer the haptic feedback. Analogous problems occur with touch sensing and the generation or sensing of audio or acoustic signals.